Getting error unknown server error while using asyncfileupload in asp net usin


ASP.NET is a popular language used for developing web applications. It provides a framework for building dynamic websites and web services. However, like any programming language, developers may encounter errors while with ASP.NET. One common error that developers may face is the “unknown server error” while using the AsyncFileUpload control.

Understanding the Error

The “unknown server error” typically occurs when is an issue with the AsyncFileUpload control in ASP.NET. This control allows users to upload files asynchronously, without causing the entire page to refresh. However, if there is an error the file upload process, this error message may be displayed.

Identifying the Cause

There can be several reasons for encountering the “unknown server error” while using the AsyncFileUpload control. Some common causes include:

  • Incorrect of the control
  • Insufficient file upload permissions
  • Server-side code

Solving the Error

To solve the “unknown server error” while using the AsyncFileUpload control, you can follow these steps:

Step 1: Check Control Configuration

Ensure that the AsyncFileUpload control is properly in your ASP.NET page. Verify that the control has the correct ID, and that the necessary event handlers are defined.

Step 2: Verify File Upload Permissions

Ensure that the necessary file upload permissions are set on the server. The ASP.NET application should have access to the where the uploaded files are stored.

Step 3: Debug Server-Side Code

If the error persists, it may be due to issues in the server-side code. Debug the code to identify any potential errors or exceptions. Check if the necessary file handling logic is implemented correctly.

protected void fileUpload_UploadedComplete(object sender, AjaxControlToolkit.AsyncFileUploadEventArgs e)
        // File handling logic here
    catch ( ex)
        // Handle exceptions and log errors


The “unknown server error” while using the AsyncFileUpload control in ASP.NET can be resolved by following the steps mentioned above. By ensuring proper control configuration, verifying file upload permissions, and debugging the server-side code, developers can overcome this error and successfully implement file uploads in their ASP.NET applications.

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